1. Field of the Invention
The present invention relates to a feedback amplifier, and more particularly, to an amplifier which uses an inverter comprising a field effect transistor (hereinafter referred to as a FET) and which can be integrated onto a gallium arsenide (GaAs) substrate or the like.
2. Description of the Prior Art
The configurations of feedback amplifiers used as microwave amplifiers are shown in the following prior art references:
(a) W. O. Camp et al "2.about.6 GHz Monolithic Microwave Amplifier" IEEE, Monolithic Circuits Symposium Digest 1983, pp 76.about.80; PA0 (b) P. N. Rigby et al "Broadband Monolithic Low-Noise Feedback Amplifiers", IEEE, Monolithic Circuits Symposium Digest 1983, pp 71.about.75; PA0 (c) K. Honjo et al "Ultra-Broad-Band GaAs Monolithic Amplifier", IEEE, MTT-30, Vol. 7, 1982, pp 27.about.1033; PA0 (d) Nishimura et al "GaAs Monolithic IC Ultra-Wideband Low-noise Amplifier" Document SSD80-90 of the Meeting for the Study of Semiconductors and Transistors of the Institute of Electronics and Communication Engineers of Japan, pp 25.about.p 30; PA0 (e) Nishiuma et al "Low-dissipation, and Low-noise GaAs Monolithic Amplifier Using New Feedback System", Document MW-82-109 of the Meeting for the Study of Micro-waves of the Institute of Electronics and Communication Engineers of Japan, pp 27.about.32; PA0 (f) Shigaki et al "GaAs Monolithic Amplifier and Oscillator" Document SSD 83-130 of the Meeting for the Study of Semiconductors and Transistors of the Institute of Electronics and Communication Engineers of Japan, pp 55.about.62; and PA0 (g) M. Abe et al "New Technology Towards GaAs LSI/VLSI for computer Application", IEEE, MTT-30, No. 7, July, 1982, pp. 992.about.998.
In the above-mentioned prior art, reference (a) discloses a monolithic microwave feedback amplifier having a frequency band of 2.about.6 GHz, reference (b) discloses a wideband monolithic low-noise feedback amplifier having a frequency band of 0.6.about.6 GHz, and references (c), (d), (e), and (f) also disclose a microwave feedback amplifier which is used in a GHz frequency range. Reference (g) discloses a technique by which a high frequency amplifier is realized by using a fully implanted planar GaAs metal semiconductor FET (MESFET).
In the microwave feedback amplifier disclosed in the above-mentioned references (a) to (f), an output from an output terminal is fed back to an input terminal through a feedback resistor and a capacitor. Moreover input and output capacitors are necessary, because the gate and drain have a constant bias voltage, and the bias voltage has to be separated from input and output DC voltage.
In the conventional feedback amplifier described above, feedback through the capacitor is performed to cancel the drain-gate potential difference across the input terminal and the output terminal. When an operating frequency is relatively high, the capacity of the capacitor can be relatively small. However, when the circuit is operated at a low frequency, for example, a frequency falling within the microwave frequency band, a capacitor having a large capacitance is required. In view of this, when the feedback amplifier as described above is formed on a GaAs integrated circuit (IC) or the like, sometimes a feedback capacitor must be externally connected to the IC. As is well known, when some parts of a circuit are separately and externally mounted to an IC, floating factors are introduced into the circuit. This is not preferable when the operating characteristics of the circuit need to be maintained.
When such a capacitor is formed on the same substrate on which the IC is formed, most of the chip area is occupied by the capacitor. Moreover, the capacitance of a capacitor which can be formed on a general square substrate having a side of several millimeters, is about 100 pF at most. Accordingly, it is impossible to obtain a feedback amplifier which can operate at a frequency of several tens of megahertz or lower.